Pipeline systems which are used to transport granular slurry materials tend to wear non-uniformly. To counteract uneven wear, and get the maximum life from such pipes, the sections of pipe are rotated on a regular basis.
In such slurry systems, pressure gages are mounted directly on the pipe to monitor fluid pressure to insure that slurry flow through the pipe is not interrupted, and to insure that pressure does not build up to unsafe levels. When the pipe sections are rotated to obtain uniform wear, the pressure gages rotate with the pipe, creating a major inconvenience in reading the gages, especially when they are disposed under the pipe sections, which are usually laid just above the ground.
In the past, the practice has been to tap a small hole in the pipewall and to mount the pressure gage directly on a pipe section in communication with the hole in the pipewall. When such pipe sections are rotated to insure even internal wear, it is necessary to remove the pressure gage, rotate the pipe section the desired amount, and then tap a new hole on the top of the pipewall. The old hole from which the pressure gage is removed is then plugged, as by welding.
The above practice is expensive, and requires coordination of pipe rotation with the availability of skilled welders, which can be an added expense because of the remote locations of the pipelines. In addition, each plugged gage mounting hole represents a potential weak point in the pipe.